iptables -t nat -A prerouting_rule -i $WAN -p udp --dport 1194 -j ACCEPT
 iptables        -A input_rule      -i $WAN -p udp --dport 1194 -j ACCEPT
 iptables -A FORWARD -i $WAN -p udp --dport 1194 -o tun0 -j ACCEPT

I tried adding

 iptables -A FORWARD -i tun0 -o vlan1 -j ACCEPT